The present invention relates generally to the field of fabricating electronic assemblies such as display panels.
Electronic assemblies such as display panels. Display panels may be comprised of active matrix or passive matrix panels are widely used. Active matrix panels and passive matrix panels may be either transmissive or reflective. Transmissive displays include polysilicon thin-film transistor (TFT) displays, and high-resolution polysilicon displays. Reflective displays typically comprise single crystal silicon integrated circuit substrates that have reflective pixels.
Liquid crystals, electroluminescent (EL) materials, organic light emitting diodes (OLEDs), up and downconverting phosphor (U/DCP), electrophoretic (EP) materials, or light emitting diodes (LEDs) may be used in fabricating flat-panel display panels. Each of these is known in the art and is discussed briefly below.
Liquid crystal displays (LCDs) may have an active-matrix backplane in which thin-film transistors are co-located with LCD pixels. Flat-panel displays employing LCDs generally include five different components or layers: a White or sequential Red, Green, Blue light source, a first polarizing filter, that is mounted on one side of a circuit panel on which the TFTs are arrayed to form pixels, a filter plate containing at least three primary colors arranged into pixels, and a second polarizing filter. A volume between the circuit panel and the filter plate is filled with a liquid crystal material. This material will rotate the polarized light when an electric field is applied between the circuit panel and a transparent ground electrode affixed to the filter plate or a cover glass. Thus, when a particular pixel of the display is turned on, the liquid crystal material rotates polarized light being transmitted through the material so that it will pass through the second polarizing filter. Some liquid crystal materials, however, require no polarizers.
LCDs may also have a passive matrix backplane. A passive matrix backplane typically includes two planes of strip electrodes that sandwich the liquid crystal material. However, passive matrices generally provide a lower quality display compared to active matrices. Liquid crystal material includes, but is not limited to, twisted nematic (TN), Super TN, double STN, and ferroelectric. U/DCP and EP displays are formed in a similar fashion except the active medium is different (e.g., upconverting gas, downconverting gas, electrophoretic materials).
EL displays have one or more pixels that are energized by an alternating current (AC) that must be provided to each pixel by row and column interconnects. EL displays generally provide a low brightness output because passive circuitry for exciting pixel phosphors typically operates at a pixel excitation frequency that is low relative to the luminance decay time of the phosphor material. However, an active matrix allows the use of higher frequency AC excitation in order to obtain brighter electroluminescence in the pixel phosphor
LED displays are also used in flat-panel displays. LEDs emit light when energized. OLEDs operate like the LEDs except OLEDs use organic material in the formation of the diode.
Regardless of the type of active medium used, displays are generally comprised of at least a substrate and a backplane. The backplane forms the electrical interconnection of the display and typically comprises electrodes, capacitors, and transistors in at least some embodiments of a backplane.
FIGS. 1A-1D illustrate a variety of displays that formed on a rigid substrate are known in the art. FIG. 1A illustrates a rigid display device in which the active matrix display backplane 10 is coupled to a rigid substrate 12. Typically, the active matrix display backplane is also rigid. FIG. 1B shows another rigid display. There, the active matrix display backplane 10 is coupled to a rigid substrate 12 (e.g., glass). Also shown is a plurality of blocks 14. These blocks may be fabricated separately and then deposited into holes on substrate 12 by a process known as fluidic self assembly; an example of this process is described in U.S. Pat. No. 5,545,291. These blocks may each contain driver circuitry (e.g., MOSFET and capacitor) for driving a pixel electrode. The active matrix backplane includes transparent pixel electrodes and row/column interconnects (not shown) to electrically interconnect blocks 14. Plurality of blocks 14 are coupled to active matrix display backplane 10 and rigid substrate 12. FIG. 1C illustrates reflective display 16 coupled to rigid substrate 12. FIG. 1D illustrates a reflective display 16 coupled to rigid substrate 12. Plurality of blocks 14 is coupled to reflective display 16 and to rigid substrate 12.
Given the brief description of some electronic assemblies such as displays, the discussion now turns to the placement of elements onto rigid substrate 12. Placing elements, such as pixel drivers, on a rigid substrate is well known. Prior techniques may be generally divided into two types: deterministic methods or random methods. Deterministic methods, such as xe2x80x9cpick and placexe2x80x9d, use a human or an arm of a robot to pick each element and place it into its corresponding location in a different substrate. Pick and place methods generally place devices one at a time and are generally not applicable to very small or numerous elements such as those needed for large arrays, such as an active matrix liquid crystal display.
Random placement techniques are more effective and result in high yields if the elements to be placed have the right shape. U.S. Pat. No. 5,545,291 describes a method that uses random placement. In this method, microstructures are assembled onto a different substrate through fluid transport. This is sometimes referred to as fluidic self-assembly (FSA). Using this technique, various blocks, each containing a functional component, may be fabricated on one substrate and then separated from that substrate and assembled onto a separate rigid substrate through FSA. The blocks that are deposited onto receptor regions of a substrate may include any of a number of different functional components, such as LEDs, pixel drivers, sensors, etc. An example of a particular type of block and its functional component is described in co-pending U.S. patent application Ser. No. 09/251,220 entitled xe2x80x9cFunctionally Symmetric Integrated Circuit Diexe2x80x9d which was filed Feb. 16, 1999 by the inventor John Stephen Smith. This application is hereby incorporated herein by reference.
As noted above, FIGS. 1B and 1D illustrate substrate 12 with blocks 14 formed in rigid substrate 12. Blocks 14 may be deposited through an FSA process. In the FSA process, a slurry containing blocks 14 is deposited over the rigid substrate 12 and blocks 14 rest in corresponding openings in substrate 12.
FIG. 2 illustrates a cross-sectional view of block 14 and circuit element 18 on the top surface of block 14. Generally, blocks 14 have a trapezoidal cross-section where the top of block 14 is wider than the bottom of block 14.
FIG. 3 illustrates a cross-sectional view of blocks 14 in recessed regions of rigid substrate 12. Between block 14 and rigid substrate 12 is eutetic layer 13.
FIG. 4 illustrates a cross-sectional view of rigid substrate 12 coupled to a rigid display backplane 30 with plurality of blocks 14 between rigid display backplane 30 and substrate 12. Plurality of blocks 14 are functionally part of display backplane 30 and are deposited onto receptor regions of substrate 12. Each block 14 drives at least one transparent pixel electrode. The electrode pixel is fabricated over a transistor that is fabricated in block 14.
FIG. 5 illustrates a top view of a portion of an array in an active matrix display backplane. Control line rows 31 and 32 in this device are coupled to gate electrodes along row and control line columns 34 and 35 are coupled to data drivers that supply pixel voltages that are applied to the pixel electrodes. Column line 34 is connected to a source electrode of field effect transistor (FET) 36. Another column line 35 is coupled to a source electrode of FET 37. Row line 32 is coupled to the gates of both FETs 36 and 37. The drain of FET 36 is coupled through capacitor 38 to a transparent pixel electrode along row 32 formed by FETs 36 and 37, and the drain of FET 37 is coupled through a capacitor to another pixel electrode along the row. In one typical example, the backplane may be formed by depositing blocks, using an FSA technique, into a rigid substrate (e.g., glass); each block contains a FET and a capacitor and is interconnected to other blocks by column and row conductors that are deposited onto the rigid substrate; and, the capacitor is coupled to a pixel electrode by another conductor that is deposited onto the rigid substrate. The active medium (e.g., a liquid crystal) is deposited at least on the pixel electrodes that will optically change the active medium""s properties in response to the combined voltages or currents produced by the pixel electrodes. The active medium at a given pixel electrode 42 typically appears as a square or dot in the overall checkerboard type matrix of the display. The actual size of the FETs and the pixel electrodes 42 are not now drawn to scale, but are shown schematically for the purposes of illustration. FIG. 6 illustrates a top view of pixel electrodes 46 on top of a substrate 48.
There are several disadvantages inherent to the related art. Rigid flat-panel displays are limited in that they are generally coupled to rigid objects. Pressure applied to flexible objects that may be coupled to rigid objects may cause too much stress on rigid flat-panel displays that could affect the electrical interconnections in rigid flat-panel displays.
Another disadvantage to these flat-panel displays is that they are manufactured in a batch operation. Batch operations inherently involve a certain amount of down lost in production. This increases production time to fabricate display panels. Additionally, flat-panel displays are generally fabricated on rigid substrates that are not continuous in length. This also decreases productivity since the assembly of the flat-panel displays is interrupted until another substrate panel is available to assemble the flat-panel display.
One aspect of the invention involves creating an electronic assembly such as a display using different sizes of blocks that may include functional components in flexible or rigid substrates.
A method for fabricating an assembly, comprising dispensing a first slurry over a substrate, said first slurry containing a plurality of first objects, and dispensing a second slurry over a substrate, said second slurry containing a plurality of second objects which are different in shape from said first shaped object, in which said first plurality of objects and said second plurality of objects are deposited onto [one of first receptor regions and second receptor regions of] said substrate.
Another aspect of the invention relates to a transfer tool having at least one transfer member for transferring more than one block from a first substrate to a second substrate.